|
| |
- What is normalization? Explain different levels of normalization?
- Check out the article Q100139 from Microsoft knowledge base and of
course, there's much more information available in the net. It'll be a good
idea to get a hold of any RDBMS fundamentals text book, especially the one
by C. J. Date. Most of the times, it will be okay if you can explain till
third normal form.
- What is denormalization and when would you go for it?
- As the name indicates, denormalization is the reverse process of
normalization. It's the controlled introduction of redundancy in to the
database design. It helps improve the query performance as the number of
joins could be reduced.
- How do you implement one-to-one, one-to-many and many-to-many
relationships while designing tables?
- One-to-One relationship can be implemented as a single table and rarely
as two tables with primary and foreign key relationships. One-to-Many
relationships are implemented by splitting the data into two tables with
primary key and foreign key relationships. Many-to-Many relationships are
implemented using a junction table with the keys from both the tables
forming the composite primary key of the junction table. It will be a good
idea to read up a database designing fundamentals text book.
- What's the difference between a primary key and a unique key?
- Both primary key and unique enforce uniqueness of the column on which
they are defined. But by default primary key creates a clustered index on
the column, where are unique creates a nonclustered index by default.
Another major difference is that, primary key doesn't allow NULLs, but
unique key allows one NULL only.
- What are user defined datatypes and when you should go for them?
- User defined datatypes let you extend the base SQL Server datatypes by
providing a descriptive name, and format to the database. Take for example,
in your database, there is a column called Flight_Num which appears in many
tables. In all these tables it should be varchar(8). In this case you could
create a user defined datatype called Flight_num_type of varchar(8) and use
it across all your tables. See sp_addtype, sp_droptype in books online.
- What is bit datatype and what's the information that can be stored
inside a bit column?
- Bit datatype is used to store boolean information like 1 or 0 (true or
false). Untill SQL Server 6.5 bit datatype could hold either a 1 or 0 and
there was no support for NULL. But from SQL Server 7.0 onwards, bit datatype
can represent a third state, which is NULL.
- Define candidate key, alternate key, composite key.
- A candidate key is one that can identify each row of a table uniquely.
Generally a candidate key becomes the primary key of the table. If the table
has more than one candidate key, one of them will become the primary key,
and the rest are called alternate keys. A key formed by combining at least
two or more columns is called composite key.
- What are defaults? Is there a column to which a default can't be bound?
- A default is a value that will be used by a column, if no value is
supplied to that column while inserting data. IDENTITY columns and timestamp
columns can't have defaults bound to them. See CREATE DEFAULT in books
online.
- What is a transaction and what are ACID properties?
- A transaction is a logical unit of work in which, all the steps must be
performed or none. ACID stands for Atomicity, Consistency, Isolation,
Durability. These are the properties of a transaction. For more information
and explanation of these properties, see SQL Server books online or any
RDBMS fundamentals text book. Explain different isolation levels An
isolation level determines the degree of isolation of data between
concurrent transactions. The default SQL Server isolation level is Read
Committed. Here are the other isolation levels (in the ascending order of
isolation): Read Uncommitted, Read Committed, Repeatable Read, Serializable.
See SQL Server books online for an explanation of the isolation levels. Be
sure to read about SET TRANSACTION ISOLATION LEVEL, which lets you customize
the isolation level at the connection level. Read Committed - A transaction
operating at the Read Committed level cannot see changes made by other
transactions until those transactions are committed. At this level of
isolation, dirty reads are not possible but nonrepeatable reads and phantoms
are possible. Read Uncommitted - A transaction operating at the Read
Uncommitted level can see uncommitted changes made by other transactions. At
this level of isolation, dirty reads, nonrepeatable reads, and phantoms are
all possible. Repeatable Read - A transaction operating at the Repeatable
Read level is guaranteed not to see any changes made by other transactions
in values it has already read. At this level of isolation, dirty reads and
nonrepeatable reads are not possible but phantoms are possible. Serializable
- A transaction operating at the Serializable level guarantees that all
concurrent transactions interact only in ways that produce the same effect
as if each transaction were entirely executed one after the other. At this
isolation level, dirty reads, nonrepeatable reads, and phantoms are not
possible.
- CREATE INDEX myIndex ON myTable(myColumn)What type of Index will get
created after executing the above statement?
- Non-clustered index. Important thing to note: By default a clustered
index gets created on the primary key, unless specified otherwise.
- What's the maximum size of a row?
- 8060 bytes. Don't be surprised with questions like 'what is the maximum
number of columns per table'. 1024 columns per table. Check out SQL Server
books online for the page titled: "Maximum Capacity Specifications". Explain
Active/Active and Active/Passive cluster configurations Hopefully you have
experience setting up cluster servers. But if you don't, at least be
familiar with the way clustering works and the two clusterning
configurations Active/Active and Active/Passive. SQL Server books online has
enough information on this topic and there is a good white paper available
on Microsoft site. Explain the architecture of SQL Server This is a very
important question and you better be able to answer it if consider yourself
a DBA. SQL Server books online is the best place to read about SQL Server
architecture. Read up the chapter dedicated to SQL Server Architecture.
- What is lock escalation?
- Lock escalation is the process of converting a lot of low level locks
(like row locks, page locks) into higher level locks (like table locks).
Every lock is a memory structure too many locks would mean, more memory
being occupied by locks. To prevent this from happening, SQL Server
escalates the many fine-grain locks to fewer coarse-grain locks. Lock
escalation threshold was definable in SQL Server 6.5, but from SQL Server
7.0 onwards it's dynamically managed by SQL Server.
- What's the difference between DELETE TABLE and TRUNCATE TABLE commands?
- DELETE TABLE is a logged operation, so the deletion of each row gets
logged in the transaction log, which makes it slow. TRUNCATE TABLE also
deletes all the rows in a table, but it won't log the deletion of each row,
instead it logs the deallocation of the data pages of the table, which makes
it faster. Of course, TRUNCATE TABLE can be rolled back. TRUNCATE TABLE is
functionally identical to DELETE statement with no WHERE clause: both remove
all rows in the table. But TRUNCATE TABLE is faster and uses fewer system
and transaction log resources than DELETE. The DELETE statement removes rows
one at a time and records an entry in the transaction log for each deleted
row. TRUNCATE TABLE removes the data by deallocating the data pages used to
store the table's data, and only the page deallocations are recorded in the
transaction log. TRUNCATE TABLE removes all rows from a table, but the table
structure and its columns, constraints, indexes and so on remain. The
counter used by an identity for new rows is reset to the seed for the
column. If you want to retain the identity counter, use DELETE instead. If
you want to remove table definition and its data, use the DROP TABLE
statement. You cannot use TRUNCATE TABLE on a table referenced by a FOREIGN
KEY constraint; instead, use DELETE statement without a WHERE clause.
Because TRUNCATE TABLE is not logged, it cannot activate a trigger. TRUNCATE
TABLE may not be used on tables participating in an indexed view
- Explain the storage models of OLAP
- Check out MOLAP, ROLAP and HOLAP in SQL Server books online for more
infomation.
- What are the new features introduced in SQL Server 2000 (or the latest
release of SQL Server at the time of your interview)? What changed between the
previous version of SQL Server and the current version?
- This question is generally asked to see how current is your knowledge.
Generally there is a section in the beginning of the books online titled
"What's New", which has all such information. Of course, reading just that
is not enough, you should have tried those things to better answer the
questions. Also check out the section titled "Backward Compatibility" in
books online which talks about the changes that have taken place in the new
version.
- What are constraints? Explain different types of constraints.
- Constraints enable the RDBMS enforce the integrity of the database
automatically, without needing you to create triggers, rule or defaults.
Types of constraints: NOT NULL, CHECK, UNIQUE, PRIMARY KEY, FOREIGN KEY. For
an explanation of these constraints see books online for the pages titled:
"Constraints" and "CREATE TABLE", "ALTER TABLE"
- What is an index? What are the types of indexes? How many clustered
indexes can be created on a table? I create a separate index on each column of
a table. What are the advantages and disadvantages of this approach?
- Indexes in SQL Server are similar to the indexes in books. They help SQL
Server retrieve the data quicker. Indexes are of two types. Clustered
indexes and non-clustered indexes. When you create a clustered index on a
table, all the rows in the table are stored in the order of the clustered
index key. So, there can be only one clustered index per table.
Non-clustered indexes have their own storage separate from the table data
storage. Non-clustered indexes are stored as B-tree structures (so do
clustered indexes), with the leaf level nodes having the index key and it's
row locater. The row located could be the RID or the Clustered index key,
depending up on the absence or presence of clustered index on the table. If
you create an index on each column of a table, it improves the query
performance, as the query optimizer can choose from all the existing indexes
to come up with an efficient execution plan. At the same t ime, data
modification operations (such as INSERT, UPDATE, DELETE) will become slow,
as every time data changes in the table, all the indexes need to be updated.
Another disadvantage is that, indexes need disk space, the more indexes you
have, more disk space is used.
- What is RAID and what are different types of RAID configurations?
- RAID stands for Redundant Array of Inexpensive Disks, used to provide
fault tolerance to database servers. There are six RAID levels 0 through 5
offering different levels of performance, fault tolerance. MSDN has some
information about RAID levels and for detailed information, check out the
RAID advisory board's homepage
- What are the steps you will take to improve performance of a poor
performing query?
- This is a very open ended question and there could be a lot of reasons
behind the poor performance of a query. But some general issues that you
could talk about would be: No indexes, table scans, missing or out of date
statistics, blocking, excess recompilations of stored procedures, procedures
and triggers without SET NOCOUNT ON, poorly written query with unnecessarily
complicated joins, too much normalization, excess usage of cursors and
temporary tables. Some of the tools/ways that help you troubleshooting
performance problems are: SET SHOWPLAN_ALL ON, SET SHOWPLAN_TEXT ON, SET
STATISTICS IO ON, SQL Server Profiler, Windows NT /2000 Performance monitor,
Graphical execution plan in Query Analyzer. Download the white paper on
performance tuning SQL Server from Microsoft web site. Don't forget to check
out sql-server-performance.com
- What are the steps you will take, if you are tasked with securing an
SQL Server?
- Again this is another open ended question. Here are some things you
could talk about: Preferring NT authentication, using server, databse and
application roles to control access to the data, securing the physical
database files using NTFS permissions, using an unguessable SA password,
restricting physical access to the SQL Server, renaming the Administrator
account on the SQL Server computer, disabling the Guest account, enabling
auditing, using multiprotocol encryption, setting up SSL, setting up
firewalls, isolating SQL Server from the web server etc. Read the white
paper on SQL Server security from Microsoft website. Also check out My SQL
Server security best practices
- What is a deadlock and what is a live lock? How will you go about
resolving deadlocks?
- Deadlock is a situation when two processes, each having a lock on one
piece of data, attempt to acquire a lock on the other's piece. Each process
would wait indefinitely for the other to release the lock, unless one of the
user processes is terminated. SQL Server detects deadlocks and terminates
one user's process. A livelock is one, where a request for an exclusive lock
is repeatedly denied because a series of overlapping shared locks keeps
interfering. SQL Server detects the situation after four denials and refuses
further shared locks. A livelock also occurs when read transactions
monopolize a table or page, forcing a write transaction to wait
indefinitely. Check out SET DEADLOCK_PRIORITY and "Minimizing Deadlocks" in
SQL Server books online. Also check out the article Q169960 from Microsoft
knowledge base.
- What is blocking and how would you troubleshoot it?
- Blocking happens when one connection from an application holds a lock
and a second connection requires a conflicting lock type. This forces the
second connection to wait, blocked on the first. Read up the following
topics in SQL Server books online: Understanding and avoiding blocking,
Coding efficient transactions. Explain CREATE DATABASE syntax Many of us are
used to creating databases from the Enterprise Manager or by just issuing
the command: CREATE DATABAE MyDB.
- But what if you have to create a database with two filegroups, one on
drive C and the other on drive D with log on drive E with an initial size of
600 MB and with a growth factor of 15%?
- That's why being a DBA you should be familiar with the CREATE DATABASE
syntax. Check out SQL Server books online for more information.
- How to restart SQL Server in single user mode? How to start SQL Server
in minimal configuration mode?
- SQL Server can be started from command line, using the SQLSERVR.EXE.
This EXE has some very important parameters with which a DBA should be
familiar with. -m is used for starting SQL Server in single user mode and -f
is used to start the SQL Server in minimal configuration mode. Check out SQL
Server books online for more parameters and their explanations.
- As a part of your job, what are the DBCC commands that you commonly use
for database maintenance?
- DBCC CHECKDB, DBCC CHECKTABLE, DBCC CHECKCATALOG, DBCC CHECKALLOC, DBCC
SHOWCONTIG, DBCC SHRINKDATABASE, DBCC SHRINKFILE etc. But there are a whole
load of DBCC commands which are very useful for DBAs. Check out SQL Server
books online for more information.
- What are statistics, under what circumstances they go out of date, how
do you update them?
- Statistics determine the selectivity of the indexes. If an indexed
column has unique values then the selectivity of that index is more, as
opposed to an index with non-unique values. Query optimizer uses these
indexes in determining whether to choose an index or not while executing a
query. Some situations under which you should update statistics: 1) If there
is significant change in the key values in the index 2) If a large amount of
data in an indexed column has been added, changed, or removed (that is, if
the distribution of key values has changed), or the table has been truncated
using the TRUNCATE TABLE statement and then repopulated 3) Database is
upgraded from a previous version. Look up SQL Server books online for the
following commands: UPDATE STATISTICS, STATS_DATE, DBCC SHOW_STATISTICS,
CREATE STATISTICS, DROP STATISTICS, sp_autostats, sp_createstats,
sp_updatestats
- What are the different ways of moving data/databases between servers
and databases in SQL Server?
- There are lots of options available, you have to choose your option
depending upon your requirements. Some of the options you have are:
BACKUP/RESTORE, dettaching and attaching databases, replication, DTS, BCP,
logshipping, INSERT...SELECT, SELECT...INTO, creating INSERT scripts to
generate data.
- Explain different types of BACKUPs avaialabe in SQL Server? Given a
particular scenario, how would you go about choosing a backup plan?
- Types of backups you can create in SQL Sever 7.0+ are Full database
backup, differential database backup, transaction log backup, filegroup
backup. Check out the BACKUP and RESTORE commands in SQL Server books
online. Be prepared to write the commands in your interview. Books online
also has information on detailed backup/restore architecture and when one
should go for a particular kind of backup.
- What is database replication? What are the different types of
replication you can set up in SQL Server?
- Replication is the process of copying/moving data between databases on
the same or different servers. SQL Server supports the following types of
replication scenarios: · Snapshot replication · Transactional replication
(with immediate updating subscribers, with queued updating subscribers) ·
Merge replication See SQL Server books online for indepth coverage on
replication. Be prepared to explain how different replication agents
function, what are the main system tables used in replication etc.
- How to determine the service pack currently installed on SQL Server?
- The global variable @@Version stores the build number of the
sqlservr.exe, which is used to determine the service pack installed. To know
more about this process visit SQL Server service packs and versions.
- What are cursors? Explain different types of cursors. What are the
disadvantages of cursors? How can you avoid cursors?
- Cursors allow row-by-row processing of the resultsets. Types of cursors:
Static, Dynamic, Forward-only, Keyset-driven. See books online for more
information. Disadvantages of cursors: Each time you fetch a row from the
cursor, it results in a network roundtrip, where as a normal SELECT query
makes only one roundtrip, however large the resultset is. Cursors are also
costly because they require more resources and temporary storage (results in
more IO operations). Further, there are restrictions on the SELECT
statements that can be used with some types of cursors. Most of the times,
set based operations can be used instead of cursors. Here is an example: If
you have to give a flat hike to your employees using the following criteria:
Salary between 30000 and 40000 -- 5000 hike Salary between 40000 and 55000
-- 7000 hike Salary between 55000 and 65000 -- 9000 hike. In this situation
many developers tend to use a cursor, determine each employee's salary and
update his salary according to the above formula. But the same can be
achieved by multiple update statements or can be combined in a single UPDATE
statement as shown below:
- UPDATE tbl_emp SET salary = CASE
WHEN salary BETWEEN 30000 AND 40000 THEN salary + 5000 WHEN salary BETWEEN
40000 AND 55000 THEN salary + 7000 WHEN salary BETWEEN 55000 AND 65000 THEN
salary + 10000 END
- Another situation in which developers tend to use cursors: You need to
call a stored procedure when a column in a particular row meets certain
condition. You don't have to use cursors for this. This can be achieved
using WHILE loop, as long as there is a unique key to identify each row. For
examples of using WHILE loop for row by row processing, check out the 'My
code library' section of my site or search for WHILE. Write down the general
syntax for a SELECT statements covering all the options. Here's the basic
syntax: (Also checkout SELECT in books online for advanced syntax).
- SELECT select_list [INTO
new_table_] FROM table_source [WHERE search_condition] [GROUP BY
group_by_expression] [HAVING search_condition] [ORDER BY order_expression [ASC
| DESC] ]
- Example
/* Use DECLARE @local_variable, DECLARE CURSOR and SET. */
DECLARE @MyVariable CURSOR
DECLARE MyCursor CURSOR FOR
SELECT LastName FROM Northwind.dbo.Employees
SET @MyVariable = MyCursor
/* Use DECLARE @local_variable and SET */
DECLARE @MyVariable CURSOR
SET @MyVariable = CURSOR SCROLL KEYSET FOR
SELECT LastName FROM Northwind.dbo.Employees
DEALLOCATE @MyCursor
- What is a join and explain different types of joins.
- Joins are used in queries to explain how different tables are related.
Joins also let you select data from a table depending upon data from another
table. Types of joins: INNER JOINs, OUTER JOINs, CROSS JOINs. OUTER JOINs
are further classified as LEFT OUTER JOINS, RIGHT OUTER JOINS and FULL OUTER
JOINS. For more information see pages from books online titled: "Join
Fundamentals" and "Using Joins".
- Can you have a nested transaction?
- Yes, very much. Check out BEGIN TRAN, COMMIT, ROLLBACK, SAVE TRAN and @@TRANCOUNT
- What is an extended stored procedure? Can you instantiate a COM object
by using T-SQL?
- An extended stored procedure is a function within a DLL (written in a
programming language like C, C++ using Open Data Services (ODS) API) that
can be called from T-SQL, just the way we call normal stored procedures
using the EXEC statement. See books online to learn how to create extended
stored procedures and how to add them to SQL Server. Yes, you can
instantiate a COM (written in languages like VB, VC++) object from T-SQL by
using sp_OACreate stored procedure. Also see books online for sp_OAMethod,
sp_OAGetProperty, sp_OASetProperty, sp_OADestroy. For an example of creating
a COM object in VB and calling it from T-SQL, see 'My code library' section
of this site.
- What is the system function to get the current user's user id?
- USER_ID(). Also check out other system functions like USER_NAME(),
SYSTEM_USER, SESSION_USER, CURRENT_USER, USER, SUSER_SID(), HOST_NAME().
- What are triggers? How many triggers you can have on a table? How to
invoke a trigger on demand?
- Triggers are special kind of stored procedures that get executed
automatically when an INSERT, UPDATE or DELETE operation takes place on a
table. In SQL Server 6.5 you could define only 3 triggers per table, one for
INSERT, one for UPDATE and one for DELETE. From SQL Server 7.0 onwards, this
restriction is gone, and you could create multiple triggers per each action.
But in 7.0 there's no way to control the order in which the triggers fire.
In SQL Server 2000 you could specify which trigger fires first or fires last
using sp_settriggerorder. Triggers can't be invoked on demand. They get
triggered only when an associated action (INSERT, UPDATE, DELETE) happens on
the table on which they are defined. Triggers are generally used to
implement business rules, auditing. Triggers can also be used to extend the
referential integrity checks, but wherever possible, use constraints for
this purpose, instead of triggers, as constraints are much faster. Till SQL
Server 7.0, triggers fire only after the data modification operation
happens. So in a way, they are called post triggers. But in SQL Server 2000
you could create pre triggers also. Search SQL Server 2000 books online for
INSTEAD OF triggers. Also check out books online for 'inserted table',
'deleted table' and COLUMNS_UPDATED()
- Example: Trigger with remainder e-mail message
-
USE pubs
IF EXISTS (SELECT name FROM sysobjects
WHERE name = 'reminder' AND type = 'TR')
DROP TRIGGER reminder
GO
CREATE TRIGGER reminder
ON titles
FOR INSERT, UPDATE, DELETE
AS
EXEC master..xp_sendmail 'MaryM',
'Don''t forget to print a report for the distributors.'
GO
- There is a trigger defined for INSERT operations on a table, in an OLTP
system. The trigger is written to instantiate a COM object and pass the newly
insterted rows to it for some custom processing. What do you think of this
implementation? Can this be implemented better?
- Instantiating COM objects is a time consuming process and since you are
doing it from within a trigger, it slows down the data insertion process.
Same is the case with sending emails from triggers. This scenario can be
better implemented by logging all the necessary data into a separate table,
and have a job which periodically checks this table and does the needful.
- What are the trigger limitations:
- The CREATE TRIGGER statement must be the first statement in the batch.
All other statements that follow in that batch are interpreted as part of
the definition of the CREATE TRIGGER statement.
- Permission to create triggers defaults to the table owner, who cannot
transfer it to other users.
- You can create a trigger only in the current database, although a
trigger can reference objects outside of the current database.
- A trigger cannot be created on a temporary or system table, although
triggers can reference temporary tables.
- INSTEAD OF DELETE and INSTEAD OF UPDATE triggers cannot be defined on a
table that has a foreign key defined with a DELETE or UPDATE action.
- Although a TRUNCATE TABLE statement is like a DELETE statement without a
WHERE clause (it deletes all rows), it does not cause DELETE triggers to
fire because the TRUNCATE TABLE statement is not logged.
- The WRITETEXT statement does not cause the INSERT or UPDATE triggers to
fire.
- What is a self join? Explain it with an example.
- Self join is just like any other join, except that two instances of the
same table will be joined in the query. Here is an example: Employees table
which contains rows for normal employees as well as managers. So, to find
out the managers of all the employees, you need a self join.
- CREATE TABLE emp ( empid int,
mgrid int, empname char(10) )
- INSERT emp SELECT 1,2,'Vyas'
INSERT emp SELECT 2,3,'Mohan' INSERT emp SELECT 3,NULL,'Shobha' INSERT emp
SELECT 4,2,'Shridhar' INSERT emp SELECT 5,2,'Sourabh'
- SELECT t1.empname [Employee],
t2.empname [Manager] FROM emp t1, emp t2 WHERE t1.mgrid = t2.empid Here's an
advanced query using a LEFT OUTER JOIN that even returns the employees
without managers (super bosses)
- SELECT t1.empname [Employee],
COALESCE(t2.empname, 'No manager') [Manager] FROM emp t1 LEFT OUTER JOIN emp
t2 ON t1.mgrid = t2.empid
- What is the difference between
stored procedure and functions?
- Stored procedures are different from
function in that they do not return
values in place of their names and they cannot be used directly in an
expression.
- Mention some cpacity specification of SQL Server 7.0/2000/2005.
-
| Object |
SQL
Server 7.0 |
SQL
Server 2000 |
|
Clustered indexes |
1 |
1 |
| Columns per Index |
16 |
16 |
| Columns per foreign/primary
Key |
16 |
16 |
| Columns per base table |
1024 |
1024 |
| Columns per select
statement |
4096 |
4096 |
| Columns per insert
statement |
1024 |
1024 |
| Databases per instance of
sql server |
32767 |
32767 |
| Foreign key table reference
per table |
253 |
253 |
| Identifier length |
128 |
128 |
| Nested Stored procedure
levels |
32 |
32 |
| Nested sub queries |
32 |
32 |
| Nested trigger levels |
32 |
32 |
| Non clustered indexes |
249 |
249 |
| Paremeter per stored
procedure |
1024 |
1024 |
| Tables per select |
256 |
256 |
| SQL Server 2005 Database Engine object |
Maximum sizes/numbers SQL Server 2005 (32-bit) |
Maximum sizes/numbers SQL Server 2005 (64-bit) |
| Batch size1 |
65,536 * Network Packet Size |
65,536 * Network Packet Size |
| Bytes per short string column |
8,000 |
8,000 |
| Bytes per GROUP BY, ORDER BY |
8,060 |
8,060 |
| Bytes per index key2 |
900 |
900 |
| Bytes per foreign key |
900 |
900 |
| Bytes per primary key |
900 |
900 |
| Bytes per row8 |
8,060 |
8,060 |
| Bytes per varchar(max), varbinary(max), xml,
text, or image column |
2^31-1 |
2^31-1 |
| Characters per ntext or nvarchar(max) column |
2^30-1 |
2^30-1 |
| Clustered indexes per table |
1 |
1 |
| Columns in GROUP BY, ORDER BY |
Limited only by number of bytes |
Limited only by number of bytes |
| Columns or expressions in a GROUP BY WITH CUBE or WITH ROLLUP
statement |
10 |
10 |
| Columns per index key7 |
16 |
16 |
| Columns per foreign key |
16 |
16 |
| Columns per primary key |
16 |
16 |
| Columns per base table |
1,024 |
1,024 |
| Columns per SELECT statement |
4,096 |
4,096 |
| Columns per INSERT statement |
1,024 |
1,024 |
| Connections per client |
Maximum value of configured connections |
Maximum value of configured connections |
| Database size |
1,048,516 terabytes |
1,048,516 terabytes |
| Databases per instance of SQL Server |
32,767 |
32,767 |
| Filegroups per database |
32,767 |
32,767 |
| Files per database |
32,767 |
32,767 |
| File size (data) |
16 terabytes |
16 terabytes |
| File size (log) |
2 terabytes |
2 terabytes |
| Foreign key table references per table4 |
253 |
253 |
| Identifier length (in characters) |
128 |
128 |
| Instances per computer |
50 instances on a stand-alone server for all SQL Server 2005 editions
except for Workgroup Edition. Workgroup Edition supports a maximum of 16
instances. SQL Server 2005 supports 25 instances on a failover cluster. |
50 instances on a stand-alone server. 25 instances on a failover
cluster. |
| Length of a string containing SQL statements (batch size)1 |
65,536 * Network packet size |
65,536 * Network packet size |
| Locks per connection |
Maximum locks per server |
Maximum locks per server |
| Locks per instance of SQL Server5 |
Up to 2,147,483,647 |
Limited only by memory |
| Nested stored procedure levels6 |
32 |
32 |
| Nested subqueries |
32 |
32 |
| Nested trigger levels |
32 |
32 |
| Nonclustered indexes per table |
249 |
249 |
| Parameters per stored procedure |
2,100 |
2,100 |
| Parameters per user-defined function |
2,100 |
2,100 |
| REFERENCES per table |
253 |
253 |
| Rows per table |
Limited by available storage |
Limited by available storage |
| Tables per database3 |
Limited by number of objects in a database |
Limited by number of objects in a database |
| Partitions per partitioned table or index |
1,000 |
1,000 |
| Statistics on non-indexed columns |
2,000 |
2,000 |
| Tables per SELECT statement |
256 |
256 |
| Triggers per table3 |
Limited by number of objects in a database |
Limited by number of objects in a database |
| UNIQUE indexes or constraints per table |
249 nonclustered and 1 clustered |
249 nonclustered and 1 clustered |
| User connections |
32,767 |
32,767 |
| XML indexes |
249 |
249 |
|
